Cytochrome P-450 catalyzed steroid hydroxylation will be studied using purified enzymes from bovine adrenal cortex and human placenta. The purified cytochrome P-450 will be reconstituted into phospholipid vesicles of varying phospholipid composition in order to define the role of the membrane in determining the substrate binding properties and catalytic activity of these enzymes. The mechanism of steroidogenic electron transport in the adrenocortical mitochondrial steroid hydroxylase systems will also be investigated using photochemical crosslinking, chemical modification, and EXAFS spectroscopy. In addition, attempts will be made to obtain crystals of the various protein components of this systems which are suitable for three-dimensional structure determination by x-ray diffraction. Finally, we will purify and characterize the protein components of the cholesterol side chain cleavage system from human placental mitochondria and compare them with the corresponding proteins from bovine adrenal cortex.